1. Field of the Invention
The present invention relates to a transfer apparatus having a link mechanism.
A wafer transfer apparatus used in the production of semiconductor devices requires that a wafer is transferred so that unwanted particles are prevented from being deposited on the wafer during the wafer transfer process. Particularly, an increase in the integration density of semiconductor devices limits the allowable values of the number and size of dust particles deposited on the wafer. Hence, it is required to prevent the existence particles in the wafer transfer apparatus and to diminish the size of the wafer transfer apparatus.
2. Description of the Prior Art
FIG. 1A is a plan view of an essential part of a conventional transfer apparatus, and FIG. 1B is a side view thereof. The transfer apparatus shown in FIGS. 1A and 1B has two driving shafts 12a and 12b mounted on a horizontal plane of a driving unit 11. Respective ends of a first pair of arms 13a and 13b are attached to the driving shafts 12a and 12b. Other ends of the first pair of arms 13a and 13b are respectively connected to a second pair of arms 15a and 15b by means of first rotary shafts 14a and 14b. Gears 16a and 16b engaging each other are fixed to other ends of the second pair of arms 15a and 15b. The other ends of the arms 15a and 15b as well as the gears 16a and 16b are fastened to a second pair of rotary shafts 18a and 18b mounted on a horizontal transfer stage 17.
In the operation of the above transfer apparatus, the driving shafts 12a and 12b are rotated by the driving unit 11, and hence a link mechanism made up of the four arms 13a, 13b, 15a and 15b moves the transfer stage 17 in the direction indicated by a two-headed arrow. The gears 16a and 16b function to equalize the turning angles of the first pair of arms 13a and 13b. More particularly, the two driving shafts 12a and 12b and the two second rotary shafts 18a and 18b are parallel to each other, and hence the turning angles of the first pair of arms 13a and 13b and the second pair of arms 15a and 15b are made to coincide with each other.
For the above-mentioned reason, the gears 16a and 16b are needed. However, there is a disadvantage in that particles are generated due to engagement of the gears 16a and 16b and are deposited to a wafer mounted on the transfer stage 17. Further, the gears 16a and 16b are structural parts of the transfer stage 17, and hence the first and second pairs of arms 13a, 13b, 15a and 15b of sufficient thickness and stiffness to support the transfer stage 17 and the gears 16a and 16b. This requires a large movement area within which the arms 13a, 13b, 15a and 15b and the transfer stage 17 are moved.